Particulates or particulate matter from a diesel engine is mainly constituted by carbonic soot and a soluble organic fraction (SOF) of high-boiling hydrocarbon and contains a trace of sulfate (misty sulfuric acid fraction). In order to suppress such kind of particulates from being discharged into atmosphere, it has been carried out that a particulate filter is incorporated in an exhaust pipe through which exhaust gas flows.
The particulate filter is a porous honeycomb structure made of ceramics such as cordierite and having lattice-like compartmentalized passages. Alternate ones of the passages have plugged inlets and the remaining passages with unplugged open inlets are plugged at their outlets. Thus, only the exhaust gas passing through the thin porous compartment walls is discharged downstream and the particulates are captured on inner surfaces of the walls.
Especially in a case of a vehicle such as tractor with short wheel bases and having various accessories laid out in mutually close relationship, it is hard to secure a new mounting space for such kind of particulate filter so as not to interfere with the accessories. As a result, it has been under review to store the particulate filter in a muffler and efficiently arrange the both of them in one and the same mounting space.
In the particulate filter, unburned ash deriving from lubricant and not removable by combustion is gradually accumulated and it is accordingly necessary to take out the particulate filter for direct cleaning such as air cleaning or water washing or to replace the same with a new filter. Thus, the particulate filter must be removably attached to the muffler.
For example, in the following Reference 1 by the same applicant as that of the invention, an exhaust emission control device has been proposed in which a box-shaped muffler has therein an inner shell arranged fixedly, a particulate filter being integrally carried by a cartridge shell and unitized into a filter cartridge which is fitted through insertion into the inner shell.                [Reference 1] JP 2003-97248A        